# Type-II superconductivity in W5Si3-type Nb5Sn2Al

## TL;DR

This paper reports the discovery of multiband, type-II superconductivity below 2.0 K in Nb5Sn2Al with a W5Si3-type structure, and compares it to related compounds to understand the factors influencing Tc.

## Contribution

It is the first report of superconductivity in Nb5Sn2Al, revealing its multiband nature and providing detailed superconducting parameters and comparisons with similar compounds.

## Key findings

- Superconductivity below 2.0 K confirmed by specific heat jump.
- Nb5Sn2Al exhibits multiband, weakly coupled, type-II superconductivity.
- Tc correlates with the average valence electrons per atom in W5Si3-type compounds.

## Abstract

We report the discovery of superconductivity in the ternary aluminide Nb$_{5}$Sn$_{2}$Al, which crystallizes in the W$_{5}$Si$_{3}$-type structure with one-dimensional Nb chains along the $c$-axis. It is found that the compound has a multiband nature and becomes a weakly coupled, type-II superconductor below 2.0 K. The bulk nature of superconductivity is confirmed by the specific heat jump, whose temperature dependence shows apparent deviation from a single isotropic gap behavior. The lower and upper critical fields are estimated to be 2.0 mT and 0.3 T, respectively. From these values, we derive the penetration depth, coherence length and Ginzburg-Landau parameter to be 516 nm, 32.8 nm and 15.6, respectively. By contrast, the isostructural compound Ti$_{5}$Sn$_{2}$Al dose not superconduct above 0.5 K. A comparison of these results with other W$_{5}$Si$_{3}$-type superconductors suggests that $T_{\rm c}$ of these compounds correlates with the average number of valence electrons per atom.